Zeolites, both natural and synthetic, have been used in a variety of catalytic and adsorptive operations. Most zeolitic materials are porous ordered aluminosilicates having a definite (although often undetermined) crystal structure. The structure may have a number of smaller cavities interconnected by a number of channels. Those cavities and channels are uniform in size within a certain zeolitic material. The above-mentioned catalytic and adsorptive processes make use of these cavities and channels by proper choice of zeolite. The zeolite channels will reject some molecules because of their size and accept others.
These zeolites typically are describable as a rigid three-dimensioned framework of silica and alumina wherein the silica and alumina tetrahedra are linked through common oxygens. The charge balance of the zeolite may be satisfied by inclusion of a proton, metal, or ammonium cation. The catalytic and adsorption properties of the zeolite may be varied by changing the ions within the zeolite. Conventional ion exchange techniques may be used to change these cations.
There are a large number of both natural and synthetic zeolitic structures. The wide breadth of such numbers may be understood by considering the work Atlas of Zeolite Structures by W. M. Meier and D. H. Olson.
Included in these zeolites is a structure known as mazzite. The mineral was first described by E. Galli in Cryst. Str. Commun.; 3, p. 339, 1974. Various synthetic mazzite-like materials have been made using a variety of techniques, mainly using tetramethylammonium (TMA) cations as templates. These synthetic mazzites are known as ZSM-4 (U.S. Pat. No. 3,923,639) and Omega (U.S. Pat. No. 4,241,036). Others have synthesized ZSM-4 using templates other than TMA, e.g., Dabco (U.S. Pat. No. 4,331,643) and choline or pyrrolidine (U.S. Pat. No. 4,021,447). There are no reported instances of making these materials using the templates or method required by this invention.
A characteristic property of the TMA-containing materials is, however, that the TMA cation is located within the small "gmelenite" cages of the structure. When these zeolites are calcined to remove the TMA templates at temperatures over 500.degree. C., structural degradation takes place, resulting in a partial loss of structural integrity and a degradation of sorption capacities and catalytic properties.
The use of quaternary ammonium salts as templates or reaction modifiers in the preparation of synthetic crystalline aluminosilicates (zeolites), first discovered by R. M. Barrer in 1961, has led to preparation of a number of zeolites not found in nature. For example, U.S. Pat. No. 4,086,859 discloses preparation of a crystalline zeolite thought to have the ferrierite structure (ZSM-21) using a hydroxyethyl-trimethyl sodium aluminosilicate gel. A review provided by Barrer in Zeolites, Vol. I, p. 136 (October, 1981) shows the zeolite types which are obtained using various ammonium organic bases as cation. In addition, Breck, Zeolite Molecular Sieves, John Wiley (New York, 1974), pp.348-378, provides a basic review of zeolites obtained using such ammonium cations in the synthesis thereof.
Other patents which are exemplitive of the use of organic ammonium-containing cationic templates include: U.S. Pat. No. 4,105,541 to Plank, et al., issued Aug. 8, 1978, which deals with production of ZSM-38 using a 2-(hydroxyalkyl)trialkylammonium compound where the alkyls are methyl or ethyl; U.S. Pat. No. 4,139,600 to Rollman, et al., issued Feb. 13, 1979, which discusses production of ZSM-5 using a tetraalkylammonium cation, the alkyl groups of which contain 2 to 5 carbon atoms; U.S. Pat. No. 4,375,458 to Dwyer, et al., issued Mar. 1, 1983, which suggests the production of ZSM-5-type zeolites by using combinations of TMA, tetraethylammonium (TEA), and tetrapropylammonium (TPA) as templates; and U.S. Pat. No. 4,287,166 to Dwyer, et al., issued Sept. 1, 1981, teaching the production of ZSM-39 using TEA, TMA or n-propylamine.
It is also known that even minor changes in the size or charge distribution of these large organic cations can induce the formation of different zeolite structures. U.S. Pat. No. 4,046,859 teaches that replacement of one of the methyl groups of the TMA compound with a hydroxy ethyl group causes the formation of a ferrierite-like phase (ZSM-21). Many such examples are enumerated by Barrer (Zeolites, 1981).
The objective of the present invention is to develop preparation methods for the synthesis of mazzite-like materials where the major organic templates are not locked into the small cavities in the structure, but are instead present in the large channels from which they can be readily removed without disruption and degradation of the host lattice. None of the literature or patents described above suggests such a material or method for making it.